Bismarck vs. Iowa

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Bgile
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Re: Bismarck vs. Iowa

Post by Bgile »

I'm sure there was a lot of testing done by the US or there wouldn't have been a Mark 8 shell, or the many mods to it which appeared as the war progressed. I believe Nathan Okun used a lot of test data as he developed his "facehard" formulas, but I don't know where he got it. He has mentioned it from time to time when he has posted.
dunmunro
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Re: Bismarck vs. Iowa

Post by dunmunro »

RobertsonN wrote:I am still a newcomer to this site and am finding it great for primary sources. In the KGV-Wikipaedia discussion, on 3 March 2010, Thorsten Wahl downloaded a 315 page report: US Naval Technical Mission to Japan (1946). This is about underwater protection. Apparently the Japanese evaluated their own, German and US systems. And the big surprise to me is that they thought the Bismarck SPS the best.
The report is here:
http://www.fischer-tropsch.org/primary_ ... S-01-9.pdf
the "Bismarck" design evaluated on document page 76, is not the design used in the Bismarck! The page 76 drawings clearly show an additional holding bulkhead inboard of the armoured bulkhead and Bismarck did not have this additional bulkhead, and so her rated defensive strength was much less than in the design evaluated by the IJN.
RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Thanks for reviving this topic. The Bismarck did have a holding bulkhead (probably 20 mm thick) from the middle platform deck to the panzer deck throughout the magazine area (including secondary and tertiary magazines). In this area the distance from the shell to the TB was generally well under 5.5 m. Throughout the boiler and turbine rooms there was no holding bulkhead but the latter distance was around 5.5 m.
Earlier in this report there appears to be a detailed account of how the Japanese arrived at the charges that a given system could withstand. At a glance I do not see how much the holding bulkhead added. I hope to read it more carefully in the future. My present understanding is that its function was limited to preventing leaks in the TB (e.g. from popped rivets) from flooding the compartment concerned and that it added little to the resistance of the system. The distance from shell to TB in the system shown is 4.5 m, so that major failure of the TB (which is what I assume exceeding the given charges would lead to) would be more likely, and resistance less, than for the 5.5 m system in Bismarck. Regarding Iowa there is a complete lack of availability of original sources giving details of tests as I've said before. Incidentally, German accounts of Jutland I have read refer to popped rivets being stopped with wooden pegs.
As to the diving shell hit on Bismarck, a holding bulkhead should have prevented the flooding inboard of the TB that occurred. However, the tears that also appeared in one of the transverse bulkheads would likely have led to some flooding anyhow. As to the system with the TB at 4.5 m, the shell had it penetrated the TB and exploded at the same location would have done much more damage inside the citadel since the TB did largely exclude splinters although not remaining watertight.
The new high temperature/high pressure machinery did not give as great space savings as the Germans had hoped for. The Scharnhorst required a vulnerable roof over the boiler rooms (i.e. the boilers were higher than expected), and during the construction of Hipper there was a two week delay when the 20 mm bulkheads had to be moved outwards (to about 3.5 m from the outer shell) because the boilers were wider than planned for (described in the Marine Arsenal issue on Hipper by Breyer). Even so, access for repairs and maintenance was very poor.
RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN »

I have now looked through this US report. At the start it says, rather surprisingly, that in 1935 systematic research on underwater protection systems in Japan was several years ahead of that in the US and UK. Different systems and types of liquid loading were tested mostly in scale tests at either 1:5.35 or 1:2.97. Protection was deemed to be no leaks in the holding bulkhead (HB). However, the HB is not further mentioned at all, so I assume its role was to stop leaks in the torpedo bulkhed (TB) and that it too would leak if the TB was ruptured.
Of particular relevance were tests at 1:2.97 of a 'single plate' system (in Table 17): 3 m from TB to outer shell, with one bulkhead between giving an outer 2.4 m wide air space and an inner 0.6 m wide space that was either also empty or liquid loaded. The joint efficiency (the ratio of joint strength to base material strength) was a quite high 0.78. Effective plate thickness is actual thickness multiplied by joint efficiency, and this was the measure of the strength of the TB. Effectiveness against a 400 kg charge of picric acid required a total bulkhead thickness of 110 mm when the inner space was left empty and 64 mm when it was 90% liquid loaded.
I can now see why the German system (p. 76) was rated so high; the TB was 50% further in and the HB a further 2 m. The actual Bismarck did not have enough space for this system but it could have accommodated a TB at 3.5 m or 4 m from the shell and an HB at 5.5 m, which would have still, according to the Japanese tests, been good. Instead they went for a rather odd system with no HB in the region of the boilers and turbines. Of the others, only the British ships had no HB (apart from for the outer engine rooms). This made the German ships quite vulnerable to leaks and is perhaps why the official rating was only 250 kg TNT, the lowest of any combatant. On the other hand, the TB was located where the HB was in most other designs, which made the TB capable of not rupturing under considerably greater charges. Friedman, in Battleship Design, talking about full scale underwater tests says that some systems, especially that of Scharnhorst, easily withstood the designed charge, and could have probably withstood a much higher charge. He does not mention leaks. Possibly, the Germans, similar to their armor scheme, traded probable non-vital damage against a lower probability of major damage (rupture of the TB or penetration of the panzer deck). It also needs to be recalled that the German and British ships had extensive compartmentation, unlike the French, Italian and US (especially NC and SD) ships, for which a leak in a machinery compartment was a serious matter.
The Iowa system is nearer to the Japanese ones in concept, with both a TB and HB. As the TB was relatively thick, a good 4 m from the outer shell at mid-draft, and the system was liquid loaded it should have been good. Weaknesses might have been a relatively narrow outer air space (the Japanese found width here to be important although it required high metacentric height to counter the resulting large off-centre flooding moment) and the upper joint efficiency, where the lower NC belt joined to the upper Class A main belt.
This report is well worthy of study by battleship enthusiasts; the translation from the original Japanese is absolutely first class. Would that there was a similar report available on their own systems.
dunmunro
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Re: Bismarck vs. Iowa

Post by dunmunro »

Of the others, only the British ships had no HB (apart from for the outer engine rooms).
There is a holding bulkhead behind the armoured bulkhead everywhere, except abreast the auxiliary machinery spaces, which themselves form a void and holding bulkhead for the main machinery spaces inboard of the auxiliary spaces. The KGV SPS is also designed to vent upward over the void-liquid-void layers, which is a feature absent from many designs, where the outer layers of the TDS are capped by the MAD or a thick HTS deck.
Bgile
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Re: Bismarck vs. Iowa

Post by Bgile »

My recollection of the report of the loss of PoW mentioned that that "venting" space was responsible for progressive flooding over the top of the TDS, and that modifications were recommended to carry the TDS up another level and not to locate things like crew facilities within it, which was the case prior to that occurance.
dunmunro
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Re: Bismarck vs. Iowa

Post by dunmunro »

Bgile wrote:My recollection of the report of the loss of PoW mentioned that that "venting" space was responsible for progressive flooding over the top of the TDS, and that modifications were recommended to carry the TDS up another level and not to locate things like crew facilities within it, which was the case prior to that occurance.
Your recollections are based upon outdated material, since the TDS was never hit and so by definition was never breached abreast the machinery spaces. An incorrect understanding of the numbers and locations of the torpedo hits and a flawed WW2 analysis led to some very incorrect theories as to the functioning of PoW's TDS, and the possibility that flooding may have occurred over the venting spaces. These theories were all shown to be incorrect by recent surveys of the wreck.
Bgile
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Re: Bismarck vs. Iowa

Post by Bgile »

dunmunro wrote:
Bgile wrote:My recollection of the report of the loss of PoW mentioned that that "venting" space was responsible for progressive flooding over the top of the TDS, and that modifications were recommended to carry the TDS up another level and not to locate things like crew facilities within it, which was the case prior to that occurance.
Your recollections are based upon outdated material, since the TDS was never hit and so by definition was never breached abreast the machinery spaces. An incorrect understanding of the numbers and locations of the torpedo hits and a flawed WW2 analysis led to some very incorrect theories as to the functioning of PoW's TDS, and the possibility that flooding may have occurred over the venting spaces. These theories were all shown to be incorrect by recent surveys of the wreck.
The ship was hit by multiple torpedoes which managed to miss the TDS? What good is it? Whether or not it happened, it does seem to be a weakness in the class. There is no doubt about the crew's washrooms being in the "vent" space, with doors leading into them.
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Re: Bismarck vs. Iowa

Post by dunmunro »

Bgile wrote:

The ship was hit by multiple torpedoes which managed to miss the TDS? What good is it? Whether or not it happened, it does seem to be a weakness in the class. There is no doubt about the crew's washrooms being in the "vent" space, with doors leading into them.
PoW was hit by 4 torpedoes, two struck near prop shafts aft of the TDS, one struck forward at the foot of the bow, and only one struck the TDS and this hit was on the starboard side abreast B turret and it does not appear to have defeated the TDS.
RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Examination of the wreck appeared to show that most damage was done by the torpedo hit aft, outside the citadel, which bent a propellor shaft that subsequently destroyed watertight integrity over a considerable length aft, as well as cutting the after ring main (power and communications cut in after half of ship). No power for part of secondary armament, some boiler rooms abandoned because of lack of ventilation in tropical conditions. Worst was the loss of the main steering mechanism. It is the case though that the only hit on the citadel appeared not to defeat the TB, unlike what was assumed at the time. I suppose it shows that torpedo hits outside the SPS can lead to loss of a ship if the SPS is not extensive enough. Littorio, at Taranto, also sank due to two hits forward. Subdivision and pumping capacity (but this needs to remain intact) are also factors.
The system of POW was evidently intended to vent upwards from the sandwich system. The deck above the sandwich was very thin. This meant it could not brace the outer bulkheads, which in turn meant they could not deflect much to absorb energy by elastic and plastic deformation, which was how most alternative systems worked. In addition the TB was not a continuous structure, being stepped in aft (there its position corresponded to the additional 20 mm bulkhead in Bismarck). Despite being the narrowest (4.1 m) and shallowest SPS, it had the highest official rating of 1000 lb TNT. I do not see how the innermost 1.5 in (1.75 in for magazine spaces) bulkhead can be classified as anything other than a TB, because it would have been subject to quite large pressure and deflection, making leaks likely. The auxiliary machinery spaces occupied 75% of the total machinery space length and the HB for the outer engine rooms was a very localized structure. The system in Vanguard was a bit wider and deeper. The KGVs were the narrowest of any WWII battleships, the original 104 ft beam being reduced by a further 1 ft, to reduce the weight of the armored deck.
Of the three modern battleships torpedoed aft, the Vittorio Veneto (with some additional damage by a near-miss bomb) was the only one to survive. And probably not by chance, since this danger had been a consideration in its design, which led to it having three rudders and well spaced propellor shafts. POW sufferred the most, ironically because of the alternating machinery layout that necessitated long wing propeller shafts.
The only modern US battleship torpedeod was NC. The main sources differ: Dulin and Garzke say the charge was over 900 lb TNT and that the SPS was defeated. Friedman says the charge was 660 lb and that the system just held. Flooding was a comparatively modest 970 tons. More serious was structural damage that all but put the foremost main turret out of action and limited sustained speed to 18 knots. Anybody know what the charge really was and whether there was flooding inboard of the HB? The performance of Iowa to a hit in this position would have likely been similar.
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Re: Bismarck vs. Iowa

Post by lwd »

RobertsonN wrote:...The only modern US battleship torpedeod was NC. The main sources differ: Dulin and Garzke say the charge was over 900 lb TNT and that the SPS was defeated. Friedman says the charge was 660 lb and that the system just held. Flooding was a comparatively modest 970 tons. More serious was structural damage that all but put the foremost main turret out of action and limited sustained speed to 18 knots. Anybody know what the charge really was and whether there was flooding inboard of the HB? The performance of Iowa to a hit in this position would have likely been similar.
From http://www.navweaps.com/Weapons/WTJAP_WWII.htm
I suspect either a Type-95 mod 1 or a Type-96 the former has a 405Kg (~900 lbs) charge the latter a 550kg (~1200lbs) charge. The charge is given as being type 97 which http://www.navweaps.com/Weapons/WTJAP_Notes.htm suggest is 107% as powerful as TNT.
The TROM at http://www.combinedfleet.com/I-19.htm states it was a Type-95.

The detailed report is not at http://www.ibiblio.org/hyperwar/USN/rep/WDR/index.html but the summary report says:
Struck by a deep-running torpedo at frame 55 port side holding bulkhead failed along a vertical butt permitting some flooding. After damage, speed was increased from 19 to 25 knots.
Here is a picture of the damage although it id's the sub as I-15 http://en.wikipedia.org/wiki/File:Torpe ... r_1942.jpg

This document http://books.google.com/books?id=oFv4gq ... do&f=false
describes the damage and lists the charge as 960 lbs which is close to 900*1.07. I believe it's the source you mention above or another work of thiers.
RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Thanks for providing a definitive answer on this one. Interesting case of serious structural damage but low shock response. Outstanding damage control. Failure to reasonably correct the list on POW meant that some AA weapons were put out of action.
For NC a case of moderate failure of the SPS, but as the effective charge was quite a lot larger than the designed one (700 lb TNT), it could be said that the system performed as expected, which I think is what it says in Friedmann's book.
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Re: Bismarck vs. Iowa

Post by lwd »

I would say the case is pretty strong but I would hesitate to call it definitive. We've seen misunderstandings and translation difficulties too often to completely discount them, especially going from Oriental to European languages.

In one sense most if not all of the TDS systems could be considered failures by late war as they simply weren't designed to keep pace with the improvements in torpedos. Even if we exclude wake followers and such if you look at an early war US arial torpedo (stats from: http://www.navweaps.com/Weapons/WTUS_WWII.htm ). It went from an ~400 lb TNT warhead early war to ~600lb of Torpex or similar explosive late war making it the equivalant of at least 900lbs of TNT. Similarly the MK-15 (for DD use) went from ~500lbs of TNT to ~800lbs of TNT or RDX the latter probably giving a punch of around 1200lbs of TNT. And the late war Mk-16 Sub torpedo had a warhead of 1,260lbs of Torpex (roughly the equivalant of 1,900lbs of TNT) or 960lbs of RDX (not sure what the TNT equivalance is but I suspect at least the equal of Tropex). As a reference the early war Type 93 (long lance) had a warhead of a bit over 1,000 lbs although it to worked up to around 1,800lbs.
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Re: Bismarck vs. Iowa

Post by Tiornu »

Friedman got the 660-lb figure from the damage report, which was based on intelligence regarding Japanese torpedoes.
The Germans actually were using 300kg charges in their submarine torpedoes, though I doubt they had any torpedoes with pure TNT; they typically added aluminum and HND, sometimes ammonium nitrate.
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Re: Bismarck vs. Iowa

Post by lwd »

http://www.navweaps.com/Weapons/WTGER_Notes.htm
gives some info on the German torpedo explosives. It lists it as only being about 7% more effective than straight TNT. I've seen others dispute this.
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